Berserk (凶暴な) is a status which is caused by a Berserk Staff which has the range of 1-1/2 of the user's magic. It can also be caused by a Berserk Sword in Fire Emblem: Genealogy of the Holy War and Fire Emblem: Thracia 776. Once inflicted upon a unit, it becomes uncontrollable by the player and makes them attack anyone and anything in movement range, including allies. When an ally is attacked, they normally cannot fight back, with the exception being Thracia 776. It can be healed with a Restore staff.
Berserk is especially a problem in Fire Emblem: The Blazing Blade in the Final Chapter where after beating the six bosses in each room, the last hall opens, and the Druid inside casts Berserk at long range to affect the party. It is recommended to get a Restore staff to counter this.
Although rare, if a boss is afflicted with Berserk status, it will cure itself in the following turn. Using it in this way will produce no benefits.